Photographic silver halide developing solutions containing calcium precipitation inhibitors



Patented Jan. 13, 1953 PHOTOGRAPHIC SILVER HALIDE DEVELOP- ING SOLUTIONSCONTAINING CALCIUM PRECIPITATION INHIBITORS Richard W. Henn, Rochester,N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., acorporation of New Jersey No Drawing. Application March 28, 1951, SerialNo. 218,073

12 Claims. 1

This invention relates to photography and particularly to methods andmaterials for preventing precipitation of calcium or other insolublesalts in photographic developers and other solutions.

The precipitation of insoluble calcium salts in water is a problem inmany industries and is particularly objectionable in the photographicindustry because of its effect on the quality of photographic films andthe usability of photographic processing solutions. The use of certaincomplex phosphates, especially polymerized sodium metaphosphate andsodium or potassium pyrophosphates, in photographic developers to reducethe formation of calcium sulfite scum on the jfilms and calciumprecipitates in the developer is known. Upon standing in aqueoussolutions, all of these phosphates gradually hydrolyze to theorthophosphates (Na3PO-4, Nan-IP04 or NaH2PO4, depending upon the pH)which not only possess no inhibiting properties but may also precipitatethe calcium themselves as the fiocculent calcium orthophosphates. Inaddition to this difiiculty, the addition of an excess of theseinhibitors to alum fixing baths as whencarried over from the developer,causes the precipitation of aluminum phosphate.

If the metaphosphate and pyrophosphate are expressed in terms of theratio of sodium oxide to phosphorus pentoxide, it will be seen thatsodium metaphosphate has the formula NazO-PzOs, and sodium pyrophosphatehas the formula 2Na20-P205.

In the copending application, SerialNo. 751,122, filed May 28, 1947, nowU. S. Patent 2,541,470, granted February 13, 1951, of whichl am a jointinventor, is disclosed the effect of various polyhydroxycarboxylic acidson calcium precipitation in aqueous solutions.

I have discovered that if diglycolic acid and it alkali metal salts areused alone or in conjunction with a phosphate of the type indicatedhereinafter, it is very much more effective in the prevention of calciumprecipitation and the precipitation of other insoluble salts than arethe polyhydroxy carboxylic acids, or any other acids previously used forthis purpose. Moreover, in certain instances in photographic developers,the acid exerts a preservative effect.

It is, therefore, an object of the present invention to provide a methodfor preventing precipitation of insoluble calcium salts in water. Afurther object is to provide a method for preventing the precipitationof calcium and the formation of acalcium sulfite scum on photographicfilms when treated in a developing bath. Other objects will appear fromthe following description of my invention.

These objects are accomplished by using either diglycolic acid alone orin conjunction with alkali metal phosphates particularly as a calciumprecipitation inhibitor. My invention includes aqueous systems,especially developer compositions, containing such compounds both in Wetand dry form.

The phosphates particularly useful in my invention, in conjunction withdiglycolic acid, for their sequestering properties, are thewater-soluble polyphosphates also known as molecularly dehydratedphosphates having less water in proportion to P205 than orthophosphoricacid. (Schwartz and Munter, Ind. & Eng. Chem., 34, 32: 1942) and(Partridge Chem. & Eng. News, 27, 21411949.) Accordingly, by the termpolyphosphate I mean the water-soluble phosphates of the general formula:cM2O-yP2O5, where M20 represents an alkali metal oxide such as sodium,potassium or ammonium oxide, and the ratio of a: to y is from 1 to 2.Included in this group are the following phosphates:

Sodium tripolyphosphate (5:3)

Sodium pyrophosphate (2:1)

Sodium tetraphosphate (3:2)

Sodium metaphosphate (1:1)

Sodium hexametaphosphate (1:1) glass Sodium pentapolyphosphate (6:5)

While the phosphates contemplated as a part of my invention have theproperty of forming soluble complexes with metal salts such as calciumand magnesium salts to a limited extent, the addition of diglycolic acidand its soluble salts to aqueous systems materially delays theprecipitation of insoluble salts and the effect obtained is greater thanexpected from the behavior of either the phosphate or diglycolic acidused alone, as will be seen from consideration of the data to besubsequently presented. The addition of diglycolic acid to aqueousdeveloping compositions produces the same effect and delays theformation of calcium sludge normally formed when calcium salts are addedas an impurity in the water or from the film in processing operations.Presumably, diglycolic acidfor-ms soluble complexes with the calciumsalts, as do' other organic acids such as those mentioned in the abovecopending application. However, the calcium complex of diglycolic acidappears to be more stable than the calcium complexes of the other acidsand of the phosphates since a developer composition containingdiglycolic acid can be held at the boiling point for from six to sevenhours without loss of its sequestering power.

Sodium hexametaphosphate and sodium pyrophosphate and various organicacids have previously been used in photographic developer compositions,and sodium tetraphosphate is disclosed in the mentioned copendinginvention for the same purpose together with various polyhydroxy acids.Similarly, diglycolic acid and its salts are useful with improvedresults as can be seen by consideration of the following comparativetests.

Acids such as ethylenediamin tetraacetic acid and triglycin materiallyaccelerate the rate of oxidation of developer solutions particularly inthe presence of minute quantities of iron. For example, a developercontaining 0.5 per cent of triglycin together with eight parts permillion of iron and two parts per million of copper caused very rapidoxidation of the developer when air was bubbled through the solution fortwo hours. When the developer was formulated with diglycolic acidinstead of triglycin, the developer withstood similar aeration for 30hours.

When sodium tetraphosphate was used alone as a sequestering agent in adeveloper composition of the type set forth in detail hereinafter atpl-I of 10, it lost 70 per cent of its activity after one hour at 95 C.When diglycolic acid was used in formulating the developer instead ofthe phopshate, no loss of activity was noted after six hours at 95 C.

These data constitute positive evidence of the improved effectiveness ofdiglycolic acid as a stabilizing agent for the prevention of calciumprecipitation on storage of developer compositions. Diglycolic acid is astronger sequestering agent than acids such as citric, gluconic andtartaric acids. For example, 50 grams of diglycolio acid incorporatedinto a liter of developer 'sequestered nine grams of calcium chlorideunder the conditions of test. At equal concentrations, soduim citratesequestered two grams; sodium gluconate, 1.5 grams; and sodium potassiumtartrate, 1.5 grams of calcium chloride. Similarly, glycolic acid had noeffect as a sequestering agent at a concentration at which diglycolicwas highly effective.

Diglycolic acid is more elfective in the prevention of calciumprecipitation in silver halide developers containing borate salts, thanin de- Velopers containing carbonate as the alkaline material; however,very useful results are obtained in either case. Typical developers towhich diglycolic acid can be added alone or in conjunction with thephosphates indicated above are the following:

Monomethyl-p-aminophenol sulfate g 2 Hydroquinone g 5 Sodium sulfitedesiccated g 100 Borax g 2 Water to liter 1 Monomethyl-p-aminophenolsulfate g 3.1 Hydroquinone g 12 Sodium sulfite, desiccated g 45 Sodiumcarbonate, desiccated g.. 67.5 Potassium bromide g.. 1.9 Water to liter1 In addition to protecting the developer against calcium precipitation,the employment of the acid of my invention particularly in conjunctionwith phosphate, will greatly reduce the tendency for aluminum phosphateto be formed in the fixing bath and will reduce the attendant sludge.

The use of these inhibitors need not be confined to the developer butmay be extended to other III IV 0707B"? QTEIYLS Monomethyl-p-aminophenolsulfata 2. 5 2.5 Hydroquinone 2. 5 2. 5 Sodium sulflte (anhydrous). 50.050.0 Sodium metaborate. 20. 0 20. 0 Diglycolic acid 50. 0 Sodiumhydroxide, 95% 30.0

Developer III was found to precipitate insoluble salt with the additionof 0.15 gram of calcium chloride per liter, while developer IV permittedthe addition of 8 grams of calcium chloride per liter withoutprecipitation even after heating and allowing the developer to stand.

The improved results obtained with a carbonate-containing developer areshown by diluting developer II above (one part of developer to two Ofwater) and then adding 50 grams of diglycolic acid and sufiicient sodiumhydroxide to neutralize the acid. As compounded, the developer wasprotected against addition of 1.5 grams of calcium chloride per liter,whereas without the addition of glycolic acid, insoluble salt wasprecipitated in the same developer by the addition of less than 0.1 gramof calcium chloride per liter,

In addition to the mentioned instability of phosphate complexes, it isdifiicult to prevent the precipitation of the large quantities ofcalcium introduced into a developer by the film when employing thepolyphosphates alone, even in high concentrations. In developersemploying metaborate as the alkaline material, optimumsequesteringobtainable with polyphosphates still results in the formation ofconsiderable calcium sludge. This sludge is almost completely preventedby the addition of diglycolic acid to supplement the action of thephosphate. In practice, the acid is generally added to the replenishersolution to compensate for the calcium salt be- Developer Replen- ReplenV isher A isber B Monomethyl-p-aminophenol sul- Grams Grams Grams fate2. 5 5. 0 5. 0 Hydroqumone 2. 5 l0. 0 10. 0 Sodium su1fite- 60. O 60. 060. 0 Sodium metaborate. 10.0 40. 0 40. 0 Sodium hydroxide 4. 0 8. 5Sodium tetraphosphate 0.5 l. 0 l. 0 Diglycolic acid 7. 5

A further characteristic of diglycolic acid when used for the preventionof the precipitation of insoluble salts in water is its effectivenessover-a wide range :of pH. For example, sodium hydroxide was added toseveral one per cent solutions of diglycolic acidto adjust the-pH overthe range of 2 to 12. Sodium fluoride was added as anindicator,:and1then as varying quantities of calcium chloride wereadded, the mixtures were allowed to stand. In the absence of :thediglycolicacid, precipitates were formed with very low concentrations ofcalcium chloride. Over the pH range of 4 through '10, 0.5 gram ofdiglycolic acid successfully sequestered 0.1 gram .of calcium ch ride.The sequestering action decreased somewhat at pI-I'values of 2 and 12. Asimilar but more pronounced effect obtained if a polyphosphate is alsopresent. Accordingly, the use of diglycolic acid as a sequestering agentis not limited to alkaline developer compositions but can be used inacid systems as well, for example, acid photographic fixing baths.Similarly, it has been found that the addition of as little ,as 0.1 percent of neutral diglycolic acid to ordinary tap water will lar lyprevent the formation of scale usually obtained in heating water, forexample, in boiler tubes.

The following examples further illustrate my invention.

EXAMPLE 1 The following compositions are packaged ready for dissolvingin one liter of water to make a photographic developing solution:

Compartment A Grams Monomethyl-p-aminophenol sulfate 5 Hydroquinone 2.5

Compartment B Grams Sodium sulfite (anhydrous) 60 Sodium metaborateDiglycolic acid 50 Sodium hydroxide 30 EXAMPLE 2 Compartment A GramsMonomethyl-p-aminophenol sulfate 10 Hydroquinone 5 Sodium tetraphosphate1 Compartment B Grams Sodium sulfite 60 Sodium metaborate 40 Sodiumhydroxide 8.5 Diglycolic acid 7.5

The chemicals are then added to one liter of water.

EXAMPLE 3 If desired, in Example 2, the diglycolic acid can be placed inCompartment A rather than in Compartment B.

EXAMPLE 4 In any of the above solid mixtures containing alkali-metalpolyphosphates, the tendency of the polyphosphate to fuse or becometacky on exposure to moist air may be overcome by mixing an inertalkali-metal sulfate, such as anhydrous sodium or potassium sulfate,with the polyphosphate. A mixture of one part of sodium tetraphosphatewith two parts of anhydrous sodium sulfate or potassium sulfate wasfound to remain free flowing upon an exposure to an atmosphere of '70per cent relative humidity for two weeks. The concentration may varyfrom one part of 6 polyphosphate in from 2 to :20 :parts .of alkalimetalsulfate.

EXAMPLE 5 Th presence of iron in some po'iyp-hosphates may causeincreased development fog. This fog may be controlled by the addition of-antifoggants such as alkali-metal bromides and iodides, or organicantifoggants such as 1,2,3-benzotriazo'1e and 'fi-nitrobenzimidazole. Asample of sodium 'hexametaphosphate containing 0.03 per cent of iron wasfound to give bad fog when added to developing solutions for high speednegative emulsions. The presence of 0.05 gram of 1,2,3- benzotriazoleper gram of sodium hex-ametaphosphate'prevented this fog.

The concentration of antifoggant may vary from 1 part of antifoggant tofrom 2 to parts of phosphate in the case of potassium iodide,1,2,3-benzotriazole and 'G-nitrobenzimidazole -nitrate and from 1 partof antifog-gant to from 0.1 to '10 parts of phosphate in the case ofpotassium bromide. I

In photographic developing solution useful results are obtained by usingfrom about 2 to 100 grams per liter of solution of diglycolic acid oritsalkali metal salts, particularly-in conjunction with from about :05to 20 grams per liter of polyphosphate. These ranges are particularlyuseful in conjunction with alkali metal tetraphospha'tes:and'hexametaphosphates.

The other polyphosphates indicated above besides sodium tetraphosphatecan be added to any of the above formulas in dry or liquid form.

Diglycolic acid can be added to the hydrazinecontaining developercompositions disclosed in the Ives application, Serial No. 192,380,filed 0ctober 26, 1950, now U. S. Patent No. 2,588,982, granted March11, 1952, and the Bean et a1. application, Serial No. 218,072, filedconcurrently herewith, which are used in making direct positive images.In this case, diglycolic acid is employed especially as a preservativeas well as functioning as a sequestering agent.

I claim:

1. An alkaline photographic developing solution comprising a silverhalide developer and a compound selected from the class consisting ofdiglycolic acid and its alkali metal salts.

2. An alkaline photographic developing solution comprising a silverhalide developer, a watersoluble alkali metal polyphosphate and acompound selected from the class consisting of diglycolic acid and itsalkali metal salts.

3. An alkaline photographic developing solution comprising a silverhalide developer, a watersoluble alkali metal polyphosphate having theformula xMzo-yPzOs where M is an alkali metal, and :c and 11 representnumbers in which the ratio of a: to y is from 1 to 2, an alkalinematerial, and a compound selected from the class consisting ofdiglycolic acid and its alkali metal salts.

4. An alkaline photographic developing solution comprising a silverhalide developer, 2. watersoluble metal salt of tetraphosphoric acid, analkaline material, and a compound selected from the class consisting ofdiglycolic acid and its alkali metal salts.

5. An alkaline photographic developing solution comprising a silverhalide developer, from .05 to 20 grams per liter of a water-solublealkali metal polyphosphate, an alkaline material, and from 2 to 100grams per liter of a compound selected from the class consisting ofdiglycolic acid and its alkali metal salts.

6. An alkaline photographic developing solution comprising a silverhalide developer, from .05 to 20 grams per liter of a water-solublealkali metal salt of tetraphosphoric acid, and from 2 to 100 grams perliter of a compound selected from the group consisting of diglycolicacid and its alkali metal salts.

7. An alkaline photographic developing solution comprising a silverhalide developer, from .05 to 20 grams per liter of a water-solublealkali metal hexametaphosphate, and from 2 to 100 grams per liter of acompound selected from the class consisting of diglycolic acid and itsalkali metal salts.

8. A photographic developer in dry form comprising a silver halidedeveloper, an alkaline material and a compound selected from the groupconsisting of diglycolic acid and its alkali metal salts.

9. A photographic developer in dry form comprising a silver halidedeveloper, an alkaline material, a compound selected from the groupconsisting of diglycolic acid and its alkali metal salts, and awater-soluble alkali metal polyphosphate.

10. A photographic developer in dry form comprising a silver halidedeveloper, sufiicient watersoluble alkali metal polyphosphate having theformula mMzO-gPzOa where M is an alkali metal, and a: and 3 representnumbers in which the ratio of x to 1! is from 1 to 2, to produce .05 to20 grams per liter in solution, a sufficient amount of a compoundselected from the class consisting of diglycolic acid and its alkalimetal salts to produce 2 to 200 grams per liter in solution, andsufficient alkaline material to produce an alkaline developer solutionwhen the mixture is dissolved in water.

11. A photographic developer in dry form comprising a silver halidedeveloper, sufficient watersoluble alkali metal salt of tetraphosphoricacid to produce .05 to 20 grams per liter in solution, a sufficientamount of a compound selected from the class consisting of diglycolicacid and its alkali metal salts to produce 2 to 200 grams per liter insolution, and sufiicient alkaline material to produce an alkalinedeveloper solution when the mixture is dissolved in water.

12. A photographic developer in dry form comprising a silver halidedeveloper, sufiicient watersoluble alkali metal hexametaphosphate toproduce .05 to 20 grams per liter in solution, a sufiicient amount of acompound selected from the class consisting of diglycolic acid and itsalkali metal salts to produce 2 to 200 grams per 'liter in solution, andsuflicient alkaline material to produce an alkaline developer solutionwhen the mixture is dissolved in water.

RICHARD W. HENN.

No references cited.

1. AN ALKALINE PHOTOGRAPHIC DEVELOPING SOLUTION COMPRISING A SILVERHALIDE DEVELOPER AND A COMPOUND SELECTED FROM THE CLASS CONSISTING OFDIGLYCOLIC ACID AND ITS ALKALI METAL SALTS.